Smoke detectors have been recognized as useful products in providing an early warning where ambient smoke increases to an undesirable level. When the predetermined level of smoke has been sensed, the detectors generate an audible or a visual alarm.
Two types of detectors are available in the retail market. One type is a so-called ion type. A second is a photoelectric type.
It has also been recognized that at times, particularly around kitchens, the ambient smoke level can increase in the absence of a dangerous fire condition. This can occur where cooking oils, for example, are temporarily overheated producing a level of smoke which will cause a nearby detector to go into alarm.
These nuisance alarms are an aggravation and are undesirable. It has also been known in the prior art ion-type detectors to provide a silencing feature which can be activated to temporarily silence the detector.
Such silencing features can be activated by a push button, for example, and can cause the unit to go out of alarm relatively quickly, for a predetermined period of time, such as ten to fifteen minutes. During this period of time, the smoke condition will usually dissipate, and at the end of the silencing period when the detector again becomes active, it will normally not go back into alarm.
One known silencing system is disclosed in Bellavia, et al. U.S. Pat. No. 4,901,056 assigned to the assignee of the present invention.
Structures of known photoelectric detectors are disclosed in Dederich, et al. U.S. Pat. No. 4,539,556, and Keeler U.S. Pat. No. 4,626,695, both of which are assigned to the assignee of the present invention. The disclosure and figures of the Dederich, et al. and Keeler patents are incorporated herein by reference.
There continues to be a need for inexpensive and effective circuitry which can ben used to silence photoelectric detectors in the event of nuisance alarms. Preferably, such circuitry would include a fairly limited number of additional low cost components beyond those components needed to implement the detector circuitry.